1. Field:
The invention relates to conveyor belts and belt filters, especially those of the type designated generally as a horizontal belt filter. The invention is more particularly directed to a guide means suitable for guiding a belt in such filters.
2. State of the Art:
Devices employing an endless belt trained about a pair of rotating drums and used to convey objects from one location to another have been known for many years. A readily recognized example of such a device is the common conveyor belt. Filters in general, and belt filters in particular, have also long been known in the art.
Belt filters typically include a porous filter medium which is arranged over a moving carrier belt. The medium is oftentimes configured as an endless web thereby facilitating its being urged in a circuitous path by the carrier belt. The belt is also generally constructed in an endless configuration. The belt is typically trained over a pair of rotating drums.
In conventional filters, a given segment of the filter medium is held in contact with the carrier belt over the working run of the carrier belt. It is thereafter removed from the carrier belt, facilitating removal of caking formed on the medium surface. The medium is then readjusted on the carrier belt prior to the beginning of the subsequent working run.
A suction means is oftentimes associated with the medium/carrier belt assembly for purposes of expediting the filtering process. In one embodiment, the suction means is positioned beneath the carrier belt. The belt defines a plurality of apertures therein which communicate the suction means with the filter medium positioned atop the belt. A conventional suction means used in this environment includes a vacuum box having a spatially restricted inlet. Proper operation of the filter requires the belt apertures to be held in registration with the inlet slot of the vacuum box.
Understandably, the task of maintaining the apertures of a moving carrier belt in register with the vacuum inlet slot is difficult, given the dynamic relationship of a belt with its driving drum. Carrier belts, due to structural peculiarities resulting from manufacture and/or prolonged wear, are oftentimes prone to follow a less than desired path around a pair of parallel rotating drums. Furthermore, the drums themselves may contribute to the problem by being less than perfect in their design, manufacture and/or orientation. Absent a perfect matching of a carrier belt with a pair of rollers, belt filters generally require adjustment or guide means adapted for correcting the belt's travel over the drums. Various structural arrangements and devices have been suggested in the art.
In U.S. Pat. No. 3,762,561 (Davis), a guide structure having a pair of rotatable spools positioned to abut against the opposing sides of a carrier belt is disclosed. The spools serve to confine the belt to within a preselected spatial orientation and location in order to permit the routineer control over the carrier belt's path. In those belt filters having two or more coplanarly arranged belts, the use of the Davis guides requires that the belts be separated one from another to provide for the mounting of the guides. More particularly, the Davis structure places the guides on the non-working, return run of the carrier belt path. The belts are separated one from another and directed to a non-coplanar orientation whereby the guides may be positioned in abutment against the opposing edges of each carrier belt. The non-coplanar orientation disclosed requires one belt to be raised above the other to obtain free edges for the guides to act upon. The orientation avoids any lateral displacement of the belt which could conceivably introduce tension and stress into the belt.
Application of lateral forces to the outer edges of a carrier belt has been shown to cause buckling in the belt structure. Furthermore, long term outer edge force applications have been shown to lead to abrasion on the leading edge together with a loss of outer edge structural integrity. Understandably, an erosion or reduced structural integrity of the outer edges reduces if not eliminates the efficacy of guides positioned proximate those edges to control the carrier belt path.
It should be recognized that in multi-belt filter arrangements, it is desired to maintain the carrier belts in an edge-to-edge abutment over the working run portion of the belt path. This abutment relationship not only retards liquid drainage between the belts, but furthermore hinders the probability that the filter medium may be drawn into the cavity between the adjacent belts and thereby be pinched. This pinching oftentimes leads to the medium rupturing or otherwise failing.
Other guide arrangements have required carrier belts of modified construction. A conventional approach of this type is illustrated in FIGS. 1 and 2. As shown in cross-section, a carrier belt is modified to include a medially positioned elongate guide strip (A) that extends along the bottom surface of the carrier belt. Positioned on opposite sides of the strip is a pair of guides labeled (B) and (C). The guides may be a pair of cylindrically shaped rollers (C), each mounted for rotation about a vertical axis (D). The rollers (C) operate to exert a laterally directed force on the guide strip (A) thereby retaining the carrier belt in a preselected path. FIG. 2 illustrates an alternate guide structure wherein a bracket device (E) as opposed to a pair of rollers constitutes the guiding members.
Guide means of the types shown in FIGS. 1 and 2 have encountered problems in the past. The manufacture of carrier belts oftentimes requires that the guide strip (A) be laminated onto the otherwise planar belt structure. The imposition of lateral forces on the guide strip by the guide rollers creates a shear stress on the bonding of the guide strip with the planar portion of the carrier belt. In operation, the lateral force applications tend to result in the delamination of the guide strip from the carrier belt. Once the integrity of the guide strip is destroyed, the ability of the guide to regulate the path of the belt is compromised, if not destroyed.
In those embodiments of the type shown in FIG. 2 wherein the guides are not rotatably mounted, the stationary guides or shoes tend to abrade away the guide strip, eventually leading to a loss in the ability of the guides to control the carrier belt path.
In many filtering operations, the requisite processing time and spatial area are constants. It has been recognized in recent years that adjusting the carrier belt's structural configuration by widening the belt while simultaneously shortening the length of the run can lead to improved process efficiencies in that the prerequisite spatial processing area is provided with lower energy requirements. The shortened carrier belt devices typically require a slower moving belt. Due to the shorter belt configuration, the amount of drag which is resultant from the vacuum pan's action in the belt, and which must be overcome in order to operate the belt, is reduced. Both considerations lead to further energy savings.
Though widened carrier belt filters have been shown to possess processing efficiencies, a complication has arisen in the manufacture of carrier belts having widths in excess of two meters. Though belts having widths approaching 4.2 meters have been manufactured overseas, such manufacture requires specialized machinery which often makes the costs of manufacture prohibitive. The conventional approach has been to mount a plurality of belts in a side-by-side arrangement to achieve the desired width. Observably, this approach introduces the potentiality of complications in that any irregularity in the path of one carrier belt effects its adjacent neighboring belts. As the irregular pathed belt is displaced laterally, it applies a laterally directed force to the carrier belt positioned contiguous to it, thereby disrupting the path of the contiguous belt. Understandably, the multiplication of the number of belts enhances the possibilities and probabilities of increased interrelationships between the plurality of belts.
The trend toward multi-belt filters has created a need for adjustment means adapted for adjusting the paths of the various carrier belts so as to achieve optimal filter efficiency.